jekyll-feed: Ampersands in a blog summary cause invalid atom

Hey,

If I put an ampersand in the leading paragraph of a blog post, it becomes part of the <summary> tag which causes the W3 validator to fail with this message:

summary should not contain HTML unless declared in the type attribute:
&

Here’s a commit which demonstrates “fixing” a blog post by removing the ampersands:

https://github.com/paulfurley/paulfurley.github.io/commit/7bbc20754353b0277fdec7c6193516195fa06f22

Cheers!